1H NMR spectra of (a) [RuIII(acac)2(py-imH)]OTf (2) and (b) RuIII(acac)2(py-im) (3) in CD3CN. Peaks A to D are assigned as acac-CH3 protons, peaks 1, 2, 3, and 5 as pyridine protons, and 4, 6, 7, and 8 as acac- or imidazole-CH protons. The letters and numbers show the corresponding signals between 2 and 3, as determined by reversible NMR titration by DBU/HOTf. Solvent and impurity peaks are denoted by asterisks (*).